Poznań is a city in central Poland on the River Warta and an important cultural and business center. It is one of Poland's oldest cities (established in 1253). It is home to Adam Mickiewicz University, the third largest university in Poland. The city is known for its annual Poznań International Fair (industrial fair), the Saint John's Fair, the Grand Theatre, and the Imperial Castle. Poznań has a prominent Jewish community, dating back to the thirteenth century and boasted one of the most important Jewish Councils in Poland. During World War II, Poznań fell under Nazi rule and many Poles were arrested or executed. In 1956, the Poznań protests demonstrated early discontent with communist rule by the USSR.